The present invention relates to a hot isostatic pressing method used for manufacturing metallic, intermetallic, ceramic, composite, hybrid, and coated articles from powdered materials. More particularly, the invention relates to a method that employs encapsulated processing, in-situ materials modification, advanced pattern-making, and surface coatings, to achieve articles with superior characteristics.
The present invention is an improvement over the invention disclosed and claimed in U.S. Pat. No. 5,770,136, the disclosure of which is hereby incorporated by reference.
Powder consolidation technology has been associated with significant improvements in the characteristics of various materials. The results have included articles with improved manufacturability and performance for such applications as aircraft, armaments, automobiles, machinery, tooling, medical devices, and other products. Articles produced using these techniques may have complex shapes, bonded coatings, special surfaces, and may require minimal, or no, post-molding processing. Problems with the prior art include in-process materials contamination resulting in degraded performance, limited opportunities for in-situ materials modification, and high manufacturing costs. The purpose of this invention is to provide a method producing a wide variety of high performance articles, in one process, at lower cost.
In the present invention particulates are mixed with binders as pressure-transmitting molding media. According to the invention, a pattern is prepared and then a mold medium, comprising a mixture of particulate and binder, is charged over the pattern to produce, after the binder has cured, a mold with the desired cavity. A powdered material is fed into the cavity conforming to the mold""s geometry. The mold serves as a pressure-transmitting medium during a consolidation process.
As an alternative, particulates are mixed with a polymer powder or a liquid polymer to form a dry mix or a wet mix. A mold is produced by beam sintering or curing the polymer, bonding the particulates into the desired shape using stereolithography (SLA).
As another alternative, particulates are mixed with a polymer powder or a liquid polymer to form a dry mix or a wet mix. A mold is produced by beam sintering or curing the polymer, bonding the particulates into the desired shape using selective laser sintering (SLS).
As yet another alternative, particulates are mixed with a polymer powder or a liquid polymer to form a dry mix or a wet mix. A mold is produced by beam sintering or curing the polymer, bonding the particulates into the desired shape using fused deposition modeling (FDM).
As yet another alternative, a mold is produced by machining blocks, made of particulate and binder, and assembling the machined blocks into a completed mold. A glue may be used to hold the blocks together.
It is an object of the invention to prevent contamination of powdered material by harmful gases released from the particulate and binder. To this end, one or more contamination eliminating materials may be included. The contamination eliminating material is selected to have an affinity for the harmful gases that, at elevated temperatures, is higher than that of the powdered material. The contamination eliminating material is added into the molding medium, or into the powdered material.
It is a further object of the invention to produce a coated article. To this end, a slurry, or a paste, or dry particles, containing the desired coating material is applied or attached to part, or all, of the surface of the cavity within the mold. Subsequently, the cavity is filled with powdered material. A high-pressure consolidation step later integrates coating and powder. The coating can be applied as single layer, or multiple layers. Each layer may be comprised of a single material or of multiple materials (phases). The coating may be solid, porous, smooth or rough. In order to produce a hybrid article, one or more inserts may be placed into the mold cavity prior to filling with powdered material.
After transferring the mold into a container, the mold is heated to an elevated temperature. The temperature profile during this initial heating phase, and the surrounding atmosphere, may be controlled for improved results. This heating cycle may serve to burn or evaporate the binder, and to eliminate contaminating gases. It may also serve to transform the powdered material partially or entirely into another material through chemical reaction. A modifying reactant may be included to participate in this chemical reaction.
The container is then covered, evacuated, and sealed. After sealing, the container is heated again and compressed isostatically at elevated temperatures to consolidate the powdered material. The mold serves as a pressure-transmitting medium. After consolidation, the material surrounding the article is removed. The article may be blasted with sand to clean its surface or etched with an acid. One phase of a coating material may be dissolved to produce a porous coating.
The present invention solves problems resulting from contamination of powdered materials by harmful gases released by particulates and binders, as well as problems encountered in lowering production cost and reducing lead time for single, and small quantity, production runs.
Diffusion bonding is a technique to bond materials together to produce specially structured articles, or to bond dissimilar materials together to produce special hybrid articles. High temperatures and pressure are required for a diffusion bonding process. This invention expands diffusion bonding to wider uses. This invention not only provides the required high temperature and pressure, but also provides the ability to bond a solid to a solid, a solid to a powder, a powder to a powder, or two or more different components at the same time. This invention also provides an easy way to bond components with various shapes and dimensions at almost any location and angle. Such bonding would otherwise be difficult, or impossible. By adding a contamination eliminating material in the mold and conducting an initial reaction heating and contamination eliminating process, the bonding surfaces of components are cleaned chemically. This results in excellent bond quality.
The major advantages of the present invention are: (1) great flexibility, (2) high product quality, (3) competitive production cost, and (4) ability to incorporate various coating and bonding steps, including in-situ porous coating and calcium phosphate material to produce medical devices.